Two things that live on your SD card and never followed Prelude when it updated.
Outdated mods now tell you. The Smash mod and the Mario Kart country flag sit on the SD
card, so shipping a newer Prelude never touched them. You updated, assumed you were current,
and kept the old mod. Prelude now checks alongside its own update check and asks you, once,
whether to refresh them.
It compares the file contents rather than their size, which matters: between mod v1.4.0 and
v1.4.1 the two files that changed kept exactly the same size, so a size check would have seen
nothing.
Nothing is offered if you never installed the mod, and nothing is offered while Prelude itself
is out of date, since updating Prelude reinstalls them anyway.
Mario Kart country flags now cover 4.0.0. Both patches are written side by side and the
console applies whichever matches your installed version, so updating the game no longer
silently drops your flag. If you already had a flag installed, the prompt above offers to add
the missing one. Flag data from alyeri/nextendo-mk8d-country-flags.
Super Mario Bros. 35 Special Battle can be installed from the rail.
Earlier in v3.4.0: SSBU Online Deluxe updated to v1.4.1, which is the release that adds
support for Smash 13.0.5.